In the past, structures for use on or in bodies of water have typically been cast in place on dry land, and then floated to the resident site and then sunk into position. Typical of these structures is that shown in the booklet published by the Prescon Corporation of San Antonio, Tex. and entitled Freyssinet Offshore, 1976. This reference discloses a number of offshore drilling platforms which are constructed of prestressed, cast in place arrays of columns which are surrounded by a perforated breakwater wall.
A significant disadvantage of such a structure is the requirement that the structure be cast in place and floated as a whole to the eventual resting site. Further, the overall shape of the platform requires complex configurations of posttensioning tendons. The large size of the finished platform presents a multitude of logistical problems in transporting the platform to its eventual resting site. Further, because such platforms are essentially a single structure, they are typically custom designed for the particular site. Finally, the customized nature of each of these platforms tends to maintain the cost of the platforms at a high level.
In known platforms with or without undersea storage tanks, such platforms are built of steel or posttensioned prestressed concrete. In such structures the tendons are primarily circular or curvilinear and of medium size. The tendons are forced, by the circumvolutions of the concrete, into many lengths and diameters and complicated intersections.